If you are convinced the monster standing next to you, has no current use to you, there is an option to kill it.

but you must take care, as the mob will not like someone stabbing away at him/her/it.

there are a few things you can do before attacking the monster that will hopefully prevent excess blood-loss
1: look at it! seems obvious no? the last line of the monsters description will have an indication of its level, relative to you,

you could defeat it without raising a sweat: 4 levels or more below you
should be easy to defeat: 3 levels below you
looks like an easy kill for you: 2 levels below you
should be fairly easy to defeat: 1 level below you
looks like a perfect match for you! i shouldnt have to explain
(i forget... someone help me): 1 level above you
might be a struggle to defeat: 2 levels above you
should be a real challenge to kill: 3 levels about you
could deafeat you without raising a sweat: 4 levels or more above you

it would be quite stupid trying to solo that last description

2: have a plan of attack. circling, stunning, healing, or whatever. the monster may be resistant to some things, and that should be factored in. you may want instant crit weapons, curatives and restoratives, or a buddy helping you out. you might even time your special abilities and use them. many hands make light work, and tmux is no different!

3: walk in with enough mana/hp. if the monster is above you, and you arent in a group with people who can match it, it would be a sensible idea to attack the monster on full hp and mp, so you can stand a better chance against it. i would never attack a monster with only 1/3 of my health... but thats me

4: have an escape plan! homesick potions, fleeing, moving out of that room. these are all sensible options (if activated at the right time of course!). fleeing and moving take a bit of time in the middle of a battle, and you need to notice when the battle is getting out of hand. if you are in a group you would want to give your friends a bit of warning so they dont get left with a death. there is a wimpy flag in the game which will automatically make you flee if your hp drops below a certain amount